DocumentType

Each Document has a doctype attribute whose value
is either null or a DocumentType object. The
DocumentType interface in the DOM Core provides an interface
to the list of entities that are defined for the document, and little
else because the effect of namespaces and the various XML schema efforts
on DTD representation are not clearly understood as of this writing.

Puts all Text nodes in the full depth of the sub-tree
underneath this Node, including attribute nodes, into a
"normal" form where only structure (e.g., elements, comments,
processing instructions, CDATA sections, and entity references)
separates Text nodes, i.e., there are neither adjacent
Text nodes nor empty Text nodes.

the interface provides access to foo
and the first declaration of bar but not the second
declaration of bar or baz. Every node in
this map also implements the Entity interface.
The DOM Level 2 does not support editing entities, therefore
entities cannot be altered in any way.

getInternalSubset

The internal subset as a string, or null if there is none.
This is does not contain the delimiting square brackets.

Note: The actual content returned depends on how much
information is available to the implementation. This may vary
depending on various parameters, including the XML processor used to
build the document.

getName

getNotations

A NamedNodeMap containing the notations declared in the
DTD. Duplicates are discarded. Every node in this map also implements
the Notation interface.
The DOM Level 2 does not support editing notations, therefore
notations cannot be altered in any way.